Liquid-crystalline medium

ABSTRACT

The invention relates to a liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, characterized in that it comprises one or more compounds of the general formula I  
                 
 
     in which R, A 1 , Z 1 , Y and L are as defined in claim  1.

[0001] The present invention relates to a liquid-crystalline medium, tothe use thereof for electro-optical purposes, and to displays containingthis medium.

[0002] Liquid crystals are used, in particular, as dielectrics indisplay devices, since the optical properties of such substances can bemodified by an applied voltage. Electro-optical devices based on liquidcrystals are extremely well known to the person skilled in the art andcan be based on various effects. Examples of such devices are cellshaving dynamic scattering, DAP (deformation of aligned phases) cells,guest/host cells, TN (twisted nematic) cells, STN (supertwisted nematic)cells, SBE (superbirefringence effect) cells and OMI (optical modeinterference) cells. The most common display devices are based on theSchadt-Helfrich effect and have a twisted nematic structure.

[0003] The liquid-crystal materials must have good chemical and thermalstability and good stability to electric fields and electromagneticradiation. Furthermore, the liquid-crystal materials should haverelatively low viscosity and give short addressing times, low thresholdvoltages and high contrast in the cells.

[0004] Furthermore, they should have a suitable mesophase, for example anematic or cholesteric mesophase for the abovementioned cells, atconventional operating temperatures, i.e. in the broadest possible rangeabove and below room temperature. Since liquid crystals are generallyused in the form of mixtures of a plurality of components, it isimportant that the components are readily miscible with one another.Further properties, such as the electrical conductivity, the dielectricanisotropy and the optical anisotropy, must satisfy differentrequirements depending on the cell type and area of application. Forexample, materials for cells having a twisted nematic structure shouldhave positive dielectric anisotropy and low electrical conductivity.

[0005] For example, media of large positive dielectric anisotropy, broadnematic phases, relatively low birefringence, very high resistivity,good UV and temperature stability and low vapour pressure are desiredfor matrix liquid-crystal displays having integrated nonlinear elementsfor switching individual pixels (MLC displays).

[0006] Matrix liquid-crystal displays of this type are known. Examplesof nonlinear elements which can be used for individual switching ofindividual pixels are active elements (i.e. transistors). This is thenreferred to as an “active matrix”, and a differentiation can be madebetween two types:

[0007] 1. MOS (metal oxide semiconductor) or other diodes on siliconwafers as substrate.

[0008] 2. Thin-film transistors (TFTs) on a glass plate as substrate.

[0009] Use of single-crystal silicon as the substrate material limitsthe display size, since even modular assembly of the variouspar-displays results in problems at the joints.

[0010] In the case of the more promising type 2, which is preferred, theelectro-optical effect used is usually the TN effect. A differentiationis made between two technologies: TFTs comprising compoundsemiconductors, such as, for example, CdSe, or TFTs based onpolycrystalline or amorphous silicon. Intensive work is being carriedout worldwide on the latter technology.

[0011] The TFT matrix is applied to the inside of one glass plate of thedisplay, whilst the other glass plate carries the transparentcounterelectrode on the inside. Compared with the size of the pixelelectrode, the TFT is very small and has virtually no adverse effect onthe image. This technology can also be extended to fullycolour-compatible image displays, where a mosaic of red, green and bluefilters is arranged in such a way that each filter element is locatedopposite a switchable pixel.

[0012] The TFT displays usually operate as TN cells with crossedpolarizers in transmission and are illuminated from the back.

[0013] The term MLC displays here covers any matrix display containingintegrated nonlinear elements, i.e., in addition to the active matrix,also displays containing passive elements, such as varistors or diodes(MIM=metal-insulator-metal).

[0014] MLC displays of this type are particularly suitable for TVapplications (for example pocket TV sets) or for high-informationdisplays for computer applications (laptops) and in automobile oraircraft construction. In addition to problems with respect to the angledependence of the contrast and the response times, problems arise in MLCdisplays owing to inadequate resistivity of the liquid-crystal mixtures[TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K. ,TAJIMA, E. , WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, September1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p.141 ff, Paris; STROMER, M., Proc. Eurodisplay 84, September 1984: Designof Thin Film Transistors for Matrix Addressing of Television LiquidCrystal Displays, p. 145 ff, Paris]. With decreasing resistance, thecontrast of an MLC display drops, and the problem of after-imageelimination can occur. Since the resistivity of the liquid-crystalmixture generally drops over the life of an MLC display owing tointeraction with the internal surfaces of the display, a high (initial)resistance is very important in order to obtain acceptable servicelives. In particular in the case of low-voltage mixtures, it washitherto not possible to achieve very high resistivities. It isfurthermore important that the resistivity increases as little aspossible with creasing temperature and after heating and/or exposure toUV radiation. Also particularly disadvantageous are the low-temperatureproperties of the mixtures from the prior art. It is required thatcrystallization and/or smectic phases do not occur, even at lowtemperatures, and that the temperature dependence of the viscosity is aslow as possible. MLC displays of the prior art thus do not satisfycurrent requirements.

[0015] There thus continues to be a great demand for MLC displays havingvery high resistivity at the same time as a broad operating temperaturerange, short response times, even at low temperatures, and low thresholdvoltage which do not have these disadvantages or only do so to a reducedextent.

[0016] In the case of TN (Schadt-Helfrich) cells-, media are desiredwhich facilitate the following advantages in the cells:

[0017] broadened nematic phase range (in particular down to lowtemperatures),

[0018] switchability at extremely low temperatures (outdoor use,automobiles, avionics),

[0019] increased stability on exposure to UV radiation (longer life).

[0020] The media available from the prior art do not enable theseadvantages to be achieved while simultaneously retaining the otherparameters.

[0021] In the case of supertwisted cells (STN), media are desired whichenable greater multiplexibility and/or lower threshold voltages and/orbroader nematic phase ranges (in particular at low temperatures). Tothis end, a further extension of the parameter latitude available(clearing point, smectic-nematic transition or melting point, viscosity,dielectric quantities, elastic quantities) is urgently desired.

[0022] The invention has the object of providing media, in particularfor MLC, TN or STN displays of this type, which do not have theabovementioned disadvantages, or only do so to a reduced extent, andpreferably at the same time have very high resistivities and lowthreshold voltages and simultaneously low values for the rotationalviscosity γ₁.

[0023] It has now been found that this object can be achieved when novelmedia are used in displays.

[0024] The invention thus relates to a liquid-crystalline medium basedon a mixture of polar compounds having positive dielectric anisotropy,characterized in that it comprises one or more compounds of the generalformula I,

[0025] in which

[0026] R is H, an alkyl or alkenyl radical having 1 to 15 carbon atomswhich is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen, it also being possible for one or more CH₂groups in these radicals to be replaced, in each case independently ofone another, by —O—,

[0027]  —CO—, —CO—O—, —O—CO— or —S—, —O—CO—O— in such a way that O atomsare not linked directly to one another,

[0028] A¹

[0029] (a) is a trans-1,4-cyclohexylene radical in which, in addition,one or more non-adjacent CH₂ groups may have been replaced by —O— and/or—S—, or a 1,4-cyclohexenylene radical,

[0030] (b) is a 1,4-phenylene radical, in which, in addition, one or twoCH groups may have been replaced by N,

[0031] (c) is a radical from the group consisting of1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl,

[0032]  where the radicals (a) and (b) may be monosubstituted orpolysubstituted by CN, CH₃ or F,

[0033] Z¹ is —CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —CH₂CH₂—, —CH═CH—, —CF₂O—,—OCF₂—, —C≡C—, —(CH₂)₄—, —CH═CH—CH₂OH₂— or a single bond,

[0034] Y is F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6carbon atoms,

[0035] L is H or F, and

[0036] m is 0 or 1

[0037] The compounds of the formula I have a broad range ofapplications. Depending on the choice of substituents, these compoundscan serve as base materials from which liquid-crystalline media arepredominantly composed; however, compounds of the formula I can also beadded to liquid-crystalline base materials from other classes ofcompound in order, for example, to modify the dielectric and/or opticalanisotropy of a dielectric of this type and/or to optimize its thresholdvoltage and/or its viscosity.

[0038] In the pure state, the compounds of the formula I are colourlessand form liquid-crystalline mesophases in a temperature range which isfavourably located for electro-optical use. They are stable chemically,thermally and to light.

Compounds of the Formula

[0039]

[0040] where X=F, Cl, CF₃, CHF₂, OCHF₂, or OCF₃, Z=H or F and ringA=1,4-cyclohexylene or 1,4-phenylene, have already been disclosed in WO91/13850.

[0041] In the novel media comprising compounds of the formula I, Y ispreferably F, Cl, OCF₃, OCHF₂, CF₃, CHFCF₃, CF₂CHF₂, C₂H₄CHF₂,CF₂CH₂CF₃, CHF₂, OCH₂CF₃, OCH₂CHF₂, OCF₂CHF₂, O(CH₂)₃CF₃, OCH₂C₂F₅,OCH₂CF₂CHF₂, OCH₂C₃F₇, OCHFCF₃, OC₂F₅, OCF₂CHFCF₃, OCH═CF₂, OCF═CF₂,OCF═CFCF₃, OCF═CF—C₂F₅, CH═CHF, CH═CF₂, CF═CF₂, CF₂OCF₃, in particularF, OCHFCF₃, OCF₃, OCHF₂, OC₂F₅, OC₃F₇, OCH═CF₂ or CF₂OCF₃.

[0042] Particular preference is given to compounds of the formula I inwhich L=F and/or m=0.

[0043] Z¹ is preferably a single bond or —CH₂CH₂—, secondarilypreferably —CH₂O—, —OCH₂, —C—CO— or —CO—O—.

[0044] If R is an alkyl radical and/or an alkoxy radical, this can bestraight-chain or branched. It is preferably straight-chain, has 2, 3,4, 5, 6 or 7 carbon atoms and accordingly is preferably ethyl, propyl,butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxyor heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy,undecoxy, dodecoxy, tridecoxy or tetradecoxy.

[0045] Oxaalkyl is preferably straight-chain 2-oxapropyl(=methoxymethyl), 2- (=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl),2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or8-oxanonyl, or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

[0046] If R is an alkyl radical in which one CH₂ group has been replacedby —CH═CH—, this can be straight-chain or branched. It is preferablystraight-chain, has 2 to 10 carbon atoms and is vinyl, IE-alkenyl or3E-alkenyl. Accordingly, it is in particular vinyl, prop-1- or -2-enyl,but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-,-4- or -5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-,-3-, -4-, -5-, -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or-8-enyl, or dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.

[0047] If R is an alkyl radical in which one CH₂ group has been replacedby —O— and one has been replaced by —CO—, these are preferably adjacent.These thus contain one acyloxy group —CO—O— or one oxycarbonyl group—O—CO—. These are preferably straight-chain and have 2 to 6 carbonatoms. Accordingly, they are in particular acetoxy, propionyloxy,butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl,propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl,2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxypropyl,3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxy-carbonylmethyl,2-(methoxycarbonyl)ethyl, 2-(ethoxy-carbonyl)ethyl,2-(propoxycarbonyl)ethyl, 3-(methoxy-carbonyl)propyl,3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

[0048] If R is an alkyl radical in which one CH₂ group has been replacedby unsubstituted or substituted —CH═CH— and an adjacent CH₂ group hasbeen replaced by CO or CO—O or O—CO, this can be straight-chain orbranched. It is preferably straight-chain and has 4 to 13 carbon atoms.Accordingly, it is in particular acryloyloxymethyl, 2-acryloyloxyethyl,3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl,6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl,9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl,2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl,5-methacryloyloxypentyl, 6-methacryloyloxyhexyl,7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl and9-methacryloyloxynonyl.

[0049] If R is an alkyl or alkenyl radical which is monosubstituted byCN or CF₃, this radical is preferably straight-chain. The substitutionby CN or CF₃ is in any desired position.

[0050] If R is an alkyl or alkenyl radical which is at leastmonosubstituted by halogen, this radical is preferably straight-chainand halogen is preferably F or Cl. In the case of multiple substitution,halogen is preferably F. The resultant radicals also includeperfluorinated radicals. In the case of monosubstitution, the fluorineor chlorine substituent can be in any desired position, but preferablyin the ω-position.

[0051] Compounds of the formula I which contain wing groups R which aresuitable for polyaddition reactions are suitable for the preparation ofliquid-crystalline polyaddition products.

[0052] Compounds of the formula I containing branched wing groups R mayoccasionally be of importance due to better solubility in the customaryliquid-crystalline base materials, but in particular as chiral dopes ifthey are optically active. Smectic compounds of this type are suitableas components for ferroelectric materials.

[0053] Compounds of the formula I having S_(A) phases are suitable, forexample, for thermally addressed displays.

[0054] Branched groups of this type generally contain not more than onechain branch. Preferred branched radicals R are isopropyl, 2-butyl(=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl(=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy,3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy,1-methylhexoxy and 1-methylheptoxy.

[0055] If R is an alkyl radical in which two or more CH₂ groups havebeen replaced by —O— and/or —CO—O—, this may be straight-chain orbranched. It is preferably branched and has 3 to 12 carbon atoms.Accordingly, it is in particular biscarboxymethyl, 2,2-biscarboxyethyl,3,3-biscarboxypropyl, 4,4-biscarboxybutyl, 5,5-biscarboxypentyl,6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl, 8,8-biscarboxyoctyl,9,9-biscarboxynonyl, 10,10-biscarboxydecyl, bis(methoxycarbonyl)methyl,2,2-bis(methoxycarbonyl)ethyl, 3,3-bis(methoxycarbonyl)propyl,4,4-bis(methoxycarbonyl)butyl, 5,5-bis(methoxycarbonyl)pentyl,6,6-bis(methoxycarbonyl)hexyl, 7,7-bis(methoxycarbonyl)heptyl,8,8-bis(methoxycarbonyl)octyl, bis(ethoxycarbonyl)methyl,2,2-bis(ethoxycarbonyl)ethyl, 3,3-bis(ethoxycarbonyl)propyl,4,4-bis(ethoxycarbonyl)butyl and 5,5-bis(ethoxycarbonyl)hexyl.

[0056] Preferred smaller groups of compounds of the formula I are thoseof the subformulae I1 to I5′ [L=H or F]:

[0057] Particular preferrence is given to the compounds of the formulaeI1 and I2.

[0058] The 1,4-cyclohexenylene group preferably has the followingstructures:

[0059] The compounds of the formula I are prepared by methods known perse, as described in the literature (for example in the standard works,such as Houben-Weyl, Methoden der Organischen Chemie,Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditionswhich are known and suitable for said reactions. Use can also be madehere of variants which are known per se.

[0060] The compounds according to the invention can be prepared, forexample, by metallating a compound of formula IA

[0061] in which R, A¹, Z¹, L and m are as defined above, andsubsequently reacting the product with a suitable electrophile, or by acoupling reaction as follows:

[0062] The invention also relates to electro-optical displays (inparticular STN or MLC displays having two plane-parallel outer plateswhich, together with a frame, form a cell, integrated nonlinear elementsfor switching individual pixels on the outer plates, and a nematicliquid-crystal mixture of positive dielectric anisotropy and highresistivity located in the cell) which contain media of this type, andto the use of these media for electro-optical purposes.

[0063] The liquid-crystal mixtures according to the invention facilitatea significant broadening of the parameter latitude available.

[0064] The achievable combinations of rotational viscosity γ₁, clearingpoint, viscosity at low temperature, thermal and UV stability anddielectric anisotropy are far superior to previous materials from theprior art.

[0065] The requirement for a high clearing point, a nematic phase at lowtemperature and a high Δε was previously only achievable to anunsatisfactory extent. Although systems such as, for example, ZLI-3119have a comparable clearing point and comparatively favourableviscosities, they have, however, a Δε of only +3.

[0066] Other mixture systems have comparable viscosities and values ofΔε, but only have clearing points in the region of 60° C.

[0067] The liquid-crystal mixtures according to the invention make itpossible to achieve clearing points of above 80°, preferably above 90°,particularly preferably above 100° C., and simultaneously dielectricanisotropy values Δε≧6, preferably ≧8, and a high value for theresistivity while retaining the nematic phase down to −20° C. andpreferably down to −30° C., particularly preferably down to −40° C.,which allows excellent STN and MLC displays to be achieved. Inparticular, the mixtures are characterized by low operating voltages.The TN thresholds are below 2.0 V, preferably below 1.6 V, particularlypreferably <1.3 V.

[0068] It goes without saying that a suitable choice of the componentsof the mixtures according to the invention also allows higher clearingpoints (for example above 110°) to be achieved at higher thresholdvoltages or lower clearing points to be achieved at lower thresholdvoltages while retaining the other advantageous properties. It islikewise possible to obtain mixtures of relatively high Δε and thusrelatively low thresholds if the viscosities are increased by acorrespondingly small amount. The MLC displays according to theinvention preferably operate in the first transmission minimum of Goochand Tarry [C. H. Gooch and H. A. Tarry, Electron. Lett. 10, 2-4, 1974;C. H. Gooch and H. A. Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975]; inthis case, a lower dielectric anisotropy in the second minimum issufficient in addition to particularly favourable electro-opticalproperties, such as, for example, high gradient of the characteristicline and low angle dependency of the contrast (German Patent 30 22 818,U.S. Pat. No. 4,398,803) at the same time threshold voltage as in ananalogous display. This allows significantly higher resistivities to beachieved in the first minimum using the mixtures according to theinvention than using mixtures containing cyano compounds. A personskilled in the art can use simple routine methods to produce thebirefringence necessary for a prespecified layer thickness of the MLCdisplay by a suitable choice of the individual components and theirproportions by weight.

[0069] The flow viscosity at 20° C. is preferably <60 mm²·s⁻¹,particularly preferably <50 mm²·s⁻¹. The nematic phase range ispreferably at least 90°, in particular at least 100°. This rangepreferably extends at least from −20° to +80°.

[0070] Measurements of the “capacity holding ratio” (HR) [S. Matsumotoet al., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SIDConference, San Francisco, June 1984, p. 304 (1984); G. Weber et al.,Liquid Crystals 5, 1381 (1989)] have shown that mixtures according tothe invention comprising compounds of the formula I exhibit aconsiderably smaller decrease in the HR with increasing temperature thando analogous mixtures in which the compounds of the formula I arereplaced by cyanophenylcyclohexanes of the formula

[0071] or esters of the formula

[0072] The liquid crystal mixtures preferably contain less than 50 wt.%, more preferably less than 35 wt. % and particularly preferably lessthan 15% wt. of cyano compounds.

[0073] The UV stability of the mixtures according to the invention isalso considerably better, i.e. they exhibit a significantly smallerdecrease in the HR on exposure to UV radiation.

[0074] The media according to the invention are preferably based on aplurality (preferably two or more) of compounds of the formula I, i.e.the proportion of these compounds is 5-95%, preferably 10-60% andparticularly preferably in the range 15-50%.

[0075] The individual compounds of the formulae I to XVI and theirsub-formulae which can be used in the media according to the inventionare either known or can be prepared analogously to the known compounds.

[0076] Preferred embodiments are indicated below:

[0077] Medium comprises compounds of the formula I in which R ispreferably ethyl, furthermore propyl, butyl or pentyl. Compounds of theformula I having short side chains R have a positive effect on theelastic constants, in particulars K₁, and give mixtures havingparticularly low threshold voltages.

[0078] Medium additionally comprises one or more compounds selected fromthe group consisting of the general formulae II to IX:

[0079] in which the individual radicals have the following meanings:

[0080] R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, in each casehaving up to 9 carbon atoms,

[0081] X⁰ is F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6carbon atoms,

[0082] Y¹ to Y⁴ are in each case, independently of one another, H or F,

[0083] r is 0 or 1.

[0084] The compound of the formula IV is preferably

[0085] Medium additionally comprises one or more compounds of theformula

[0086] where

[0087] Medium additionally comprises one or more compounds of theformulae RI and/or RII:

[0088]  in which R⁰ is as defined above, preferably straight-chain alkylhaving 1-6 carbon atoms, and alkenyl and alkenyl are preferably, each,independently of one another, vinyl, 1E-alkenyl, 3E-alkenyl or 4-alkenylhaving up to 9 carbon atoms.

[0089] Medium additionally comprises one or more compounds selected fromthe group consisting of the general formulae X to XVI:

[0090] in which

[0091] R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, in each casehaving up to 9 carbon atoms,

[0092] X⁰ is F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6carbon atoms,

[0093] Y¹ and Y² are in each case, independently of one another H or F.

[0094] Preferably, R⁰, X⁰, Y¹ and Y² are F, Cl, CF₃, OCHF₂, alkyl,oxaalkyl, fluro-alkyl or alkenyl, in each case having up to 6 carbonatoms, where consistent with the above definitions.

[0095] The proportion of compounds of the formulae I to IX together isat least 50% by weight in the total mixture;

[0096] The proportion of compounds of the formula I is from 10 to 50% byweight in the total mixture;

[0097] The proportion of compounds of the formulae II to IX is from 20to 80% by weight in the total mixture

[0098] The medium comprises compounds of the formulae II, III, IV, V,VI, VII, VIII and/or IX

[0099] R⁰ is straight-chain alkyl or alkenyl having 2 to 7 carbon atoms

[0100] The medium essentially consists of compounds of the formulae I toIX

[0101] The medium comprises further compounds, preferably selected fromthe following group consisting of the general formulae XVII to XXII:

[0102]  in which R⁰, X⁰ and X^(0′) are as defined above, and the1,4-phenylene rings may be substituted by CN, chlorine or fluorine.

[0103] The 1,4-phenylene rings are preferably monosubstituted orpolysubstituted by fluorine atoms.

[0104] The I:(II+III+IV+V+VI+VII+VIII+IX) weight ratio is preferablyfrom 1:10 to 10:1

[0105] Medium essentially consists of compounds selected from the groupconsisting of the general formulae I to XXII.

[0106] It has been found that even a relatively small proportion ofcompounds of the formula I mixed with conventional liquid-crystalmaterials, but in particular with one or more compounds of the formulaeII to IX, results in a significant reduction in the rational viscosityand in low birefringence values, and at the same time broad nematicphases with low smectic-nematic transition temperatures are observed,thus improving the shelf life. The compounds of the formulae I to IX arecolourless, stable and readily miscible with one another and with otherliquid-crystal materials.

[0107] The term “alkyl” covers straight-chain and branched alkyl groupshaving 1-7 carbon atoms, in particular the straight-chain groups methyl,ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2-5 carbonatoms are generally preferred.

[0108] The term “alkenyl” or “alkenyl” covers straight-chain andbranched alkenyl groups having 2-7 carbon atoms, in particular thestraight-chain groups. Particular alkenyl groups are C₂-C₇-1E-alkenyl,C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, inparticular C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl.Examples of preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl,1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl;3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl,4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5carbon atoms are generally preferred.

[0109] The term “fluoroalkyl” preferably covers straight-chain groupscontaining terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl,3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and7-fluoroheptyl. However, other positions of the fluorine are notexcluded.

[0110] The term “oxaalkyl” preferably covers straight-chain radicals ofthe formula C_(n)H_(2n+1)—O—(CH₂)_(m), in which n and m are each,independently of one another, from 1 to 6, n is preferably 1 and m ispreferably from 1 to 6.

[0111] Through a suitable choice of the meanings of R⁰ and X⁰, theaddressing times, the threshold voltage, the gradient of thetransmission characteristic lines, etc., can be modified as desired. Forexample, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxyradicals and the like generally give shorter addressing times, improvednematic tendencies and a higher ratio between the elastic constants k₃₃(bend) and k₁₁ (splay) compared with alkyl and alkoxy radicals.4-Alkenyl radicals, 3-alkenyl radicals and the like generally give lowerthreshold voltages and lower values of k₃₃/k₁₁ compared with alkyl andalkoxy radicals.

[0112] A —CH₂CH₂— group in Z¹ generally results in higher values ofk₃₃/k₁₁ compared with a simple covalent bond. Higher values of k₃₃/k₁₁facilitate, for example, flatter transmission characteristic lines in TNcells with a 90° twist (for achieving grey tones) and steepertransmission characteristic lines in STN, SBE and OMI cells (greatermultiplexibility), and vice versa.

[0113] The optimum mixing ratio of the compounds of the formulae I andII+III+IV+V+VI+VII+VIII+IX depends substantially on the desiredproperties, on the choice of the components of the formulae I, II, III,IV, V, VI, VII, VIII and/or IX and on the choice of any other componentswhich may be present. Suitable mixing ratios within the abovementionedrange can easily be determined from case to case.

[0114] The total amount of compounds of the formulae I to XVI in themixtures according to the invention is not crucial. The mixtures maytherefore contain one or more further components in order to optimizevarious properties. However, the effect observed on the addressing timesand the threshold voltage is generally greater the higher the totalconcentration of compounds of the formulae I to XVI.

[0115] In a particularly preferred embodiment, the media according tothe invention comprise compounds of the formulae II to IX (preferably IIand/or III) in which X⁰ is OCF₃, OCHF₂, F, OCH═CF₂, OCF═CF₂ orOCF₂—CF₂H. A favourable synergistic effect with the compounds of theformula I results in particularly advantageous properties.

[0116] The construction of the MLC display according to the inventionfrom polarizers, electrode base plates and electrodes with surfacetreatment corresponds to the construction which is conventional fordisplays of this type. The term conventional construction here isbroadly drawn and also covers all derivatives and modifications of theMLC display, in particular also matrix display elements based on poly-SiTFTs or MIMs.

[0117] An essential difference between the displays according to theinvention and those customary hitherto based on the twisted nematic cellis, however, the choice of the liquid-crystal parameters in theliquid-crystal layer.

[0118] The liquid-crystal mixtures which can be used according to theinvention are prepared in a manner which is conventional per se. Ingeneral, the desired amount of the components used in the lesser amountis dissolved in the components making up the principal constituent,expediently at elevated temperature. It is also possible to mixsolutions of the components in an organic solvent, for example inacetone, chloroform or methanol, and, after thorough mixing, to removethe solvent again, for example by distillation.

[0119] The dielectrics may also contain other additives known to thoseskilled in the art and described in the literature. For example, 0-15%of pleochroic dyes or chiral dopes can be added.

[0120] C denotes a crystalline phase, S a smectic phase, S_(c) a smecticC phase, N a nematic phase and I the isotropic phase.

[0121] V₁₀ denotes the voltage for 10% transmission (view angleperpendicular to the plate surface). t_(on) denotes the switch-on timeand t_(off) the switch-off time at an operating voltage corresponding to2.5 times the value of V₁₀. Δn denotes the optical anisotropy and no therefractive index. Δε denotes the dielectric anisotropy (Δε=ε∥−ε⊥, whereε∥ is the dielectric constant parallel to the longitudinal molecularaxes and ε⊥ is the dielectric constant perpendicular thereto). Theelectro-optical data were measured in a TN cell at the 1st minimum (i.e.at a d·Δn value of 0.5) at 20° C., unless expressly stated otherwise.The optical data were measured at 20° C., unless expressly statedotherwise.

[0122] In the present application and in the examples below, thestructures of the liquid-crystal compounds are indicated by acronyms,with the transformation into chemical formulae taking place inaccordance with Tables A and B below. All radicals C_(n)H_(2n+1) andC_(m)H_(2m+1) are straight-chain alkyl radicals containing n or m carbonatoms respectively. The coding in Table B is self-evident. In Table A,only the acronym for the base structure is given. In individual cases,the acronym for the base structure is followed, separated by a hyphen,by a code for the substituents R¹, R², L¹ and L²: Code for R¹, R², L¹,L² R¹ R² L¹ L² nm C_(n)H_(2n+1) C_(m)H_(2m+1) H H nOm C_(n)H_(2n+1)OC_(m)H_(2m+1) H H nO.m OC_(n)H_(2n+1) C_(m)H_(2m+1) H H n C_(n)H_(2n+1)CN H H nN.F C_(n)H_(2n+1) CN H F nF C_(n)H_(2n+1) F H H nOFOC_(n)H_(2n+1) F H H nCl C_(n)H_(2n+1) Cl H H nF.F C_(n)H_(2n+1) F H FnF.F.F C_(n)H_(2n+1) F F F nCF₃ C_(n)H_(2n+1) CF₃ H H nOCF₃C_(n)H_(2n+1) OCF₃ H H nOCF₂ C_(n)H_(2n+1) OCHF₂ H H nS C_(n)H_(2n+1)NCS H H rVsN C_(n)H_(2n+1)—CH═CH—C₈H₂₅— CN H H rEsNC_(n)H_(2n+1)—O—C₂H₂₅— CN H H nAm C_(n)H_(2n+1) COOC_(m)H_(2m+1) H HnOCCF₂.F.F C_(n)H_(2n+1) OCH₂CF₂H F F

[0123] Preferred mixture components are shown in Tables A and B. TABLE A

PYP PYRP

BCH CBC

CCH CCP

CPTP

CEPTP

ECCP CECP

EPCH PCH

PTP BECH

EBCH CPC

B FET-nF

CGG CGU

CUP CDU

[0124] TABLE B

BCH-n.Fm GGP-n-Cl

Inm T-n FCIF

CBC-nmF

ECCH-nm CCH-n1EM

T-nFm CGU-n-F

PGU-n-F

CCGU-n-F

[0125] The examples below are intended to illustrate the inventionwithout representing a limitation. Above and below, percentages arepercent by weight. All temperatures are given in degrees Celsius. m.p.denotes melting point, c.p.=clearing point. Furthermore, C=crystallinestate, N=nematic phase, S=smectic phase and I=isotropic phase. The databetween these symbols represent the transition temperatures. Δn denotesthe optical anisotropy (589 nm, 20° C.), and the flow viscosity(mm²/sec) was determined at 20° C.

MIXTURE EXAMPLES Example 1

[0126] ECCP-3F.F 7.0% S → N [° C.]: >−30 ECCP-5F.F 10.0% Clearing point[° C.]: +106.5° C. BCH-3F.F.F 11.0% Δn [589 nm, 20° C.]: +0.1468BCH-5F.F.F 12.0% V_((10,0,20)) [V]: 1.54 BCH-32 5.0% γ₁ [mPa.s]: 242BCH-52 3.0% BCH-2F.F 9.0% BCH-BF.F 9.0% BCH-5F.F 9.0% PGU-3-F 17.0%CBC-33 3.0% CBC-53 3.0% CBC-55 2.0%

Example 2

[0127] CGU-2-F 10.0% S → N [° C.]: <−40.0 CGU-3-F 10.0% Clearing point[° C.]: +69.5° C. CGU-5-F 4.0% Δn [589 nm, 20° C.]: +0.1110 PGU-2-F 8.0%Δε [1 kHz, 20° C.]: 12.0 PGU-3-F 10.0% K₃/K₁ [20° C.] 1.28 CCP-30CF₃8.0% γ₁ [20° C.] [mPa.s] 171 CCP-50CF₃ 8.0% V_((10,0,20)) [V]: 1.10CCP-2F.F.F 12.0% CCP-3F.F.F 10.0% CCP-20CF₃.F 10.0% CCP-30CF₃.F 7.0%CBC-33F 3.0%

Example 3

[0128] CGH-34 5.0% S → N [° C.]: <−20.0 CGU-2-F 6.0% Clearing point [°C.]: +67.50° C. CGU-3-F 9.0% Δn [589 nm, 20° C.]: +0.1131 CGU-5-F 7.0%V_((10,0,20)) [V]: 1.09 CCP-20CF₃.F 8.0% CCP-30CF₃.F 11.0% CCP-2F.F.F11.0% CCP-3F.F.F 10.0% CCP-30CF₃ 8.0% PGU-2-F 10.0% PGU-3-F 12.0%CBC-33F 3.0%

Example 4

[0129] CGU-2-F 9.0% S → N [° C.]: <−40.0 CGU-3-F 9.0% Clearing point [°C.]: +72.5° C. CGU-5-F 2.0% Δn [589 nm, 20° C.]: +0.1220 CCP-30CF₃.F11.0% Δε [1 kHz, 20° C.]: +13.1 CCP-2F.F.F 12.0% γ₁ [20° C.] [mPa.s]:155 CCP-3F.F.F 10.0% V_((10,0,20)) [V]: 1.07 CCP-30CF₃ 8.0% CCP-50CF₃7.0% PGU-2-F 10.0% PGU-3-F 10.0% PGU-5-F 7.0% CBC-33F 5.0%

Example 5

[0130] CGU-2-F 8.0% S → N [° C.]: <−30.0 CGU-3-F 10.0% Clearing point [°C.]: +69.0° C. CGU-5-F 10.0% Δn [589 nm, 20° C.]: +0.1415 BCH-5F.F.F11.0% Δε [1 kHz, 20° C.]: +14.0 BCH-5F.F 8.0% γ₁ [20° C.] [mPa.s]: 184CCP-30CF₃ 8.0% V_((10,0,20)) [V]: 1.02 CCP-50CF₃ 7.0% PGU-2-F 10.0%PGU-3-F 10.0% PGU-3-F 12.0% CBC-33F 4.0% CBC-33F 2.0%

Example 6

[0131] CGU-2-F 6.0% S → N [° C.]: <−30.0 CGU-3-F 10.0% Clearing point [°C.]: +69.5° C. CGU-5-F 9.0% Δn [589 nm, 20° C.]: +0.1209 BCH-3F.F.F 7.0%Δε [1 kHz, 20° C.]: +15.1 CCP-30CF₃.F 6.0% γ₁ [20° C.] [mPa.s]: 185CCP-3F.F.F 9.0% V_((10,0,20)) [V]: 0.98 CCP-30CF₃ 8.0% PGU-2-F 10.0%PGU-3-F 12.0% CCZU-2-F 6.0% CCZU-3-F 14.0% CBC-33 3.0%

Example 7

[0132] CGU-2-F 11.0% S → N [° C.]: <−40.0 CGU-3-F 9.0% Clearing point [°C.]: +70.5° C. CGU-5-F 0.0% Δn [589 nm, 20° C.]: +0.1209 CCP-2F.F.F11.0% Δε [1 kHz, 20° C.]: +14.9 CCP-3F.F.F 4.0% γ₁ [20° C.] [mPa.s]: 162CCZU-3-F 15.0% V_((10,0,20)) [V]: 0.95 CCZU-5-F 6.0% CCP-30CF₃ 7.0%CCP-50CF₃ 4.0% PGU-2-F 10.0% PGU-3-F 10.0% PGU-5-F 8.0% CBC-33F 5.0%

Example 8

[0133] GGP-5-Cl 14.0% T₇3FCIF 10.0% Clearing point [° C]: 111.0° C.PGU-2-F 5.0% Δn [589 nm, 20° C.]: +0.2076 PGU-3-F 8.0% V_((10,0,20))[V]: 1.92 PGU-5-F 6.0% FET-2Cl 10.0% FET-3Cl 8.0% CGU-2-F 8.0% BCH-3F.F3.0% BCH-5F.F 12.0% CCGU-3-F 7.0% CBC-33 3.0% CBC-53 3.0% CBC-55 3.0%

Example 9

[0134] GGP-5-Cl 15.00% Clearing point [° C]: +110.0° C. T-3FClF 12.00%Δn [589 nm, 20° C.]: −0.2081 T-5FClF 4.00% V_((10,0,20)) [V]: 2.00PGU-2-F 6.00% PGU-3-F 10.00% PGU-5-F 13.00% BCH-2F.F 12.00% BCH-5F.F.F12.00% CCGU-3-F 7.00% CBC-33 3.00% CBC-53 3.00% CBC-55 3.00%

Example 10

[0135] GGP-5-Cl 14.00% Clearing point [° C.]: +110.0° C. T-3FClF 10.00%Δn [589 nm, 20° C.]: +0.2056 PGU-2-F 4.00% V_((10,0,20)) [V]: 1.87PGU-3-F 8.00% PGU-5-F 12.00% FET-2Cl 5.00% FET-3Cl 8.00% CGU-3-F 5.00%BCH-2F · F 7.00% BCH-3F · F 6.00% BCH-5F · F 6.00% CCGU-3-F 6.00% CBC-333.00% CBC-53 3.00% CBC-55 3.00%

Example 11

[0136] GGP-3-Cl 13.00% Clearing point [° C.]: +104.0° C. GGP-5-Cl 13.00%Δn [589 mm, 20° C.]: +0.2145 T-3FClF 8.00% V_((10,0,20)) [V]: 2.14FET-2Cl 12.00% FET-3Cl 8.00% FET-5Cl 13.00% BCH-2F · F 12.00% BCH-5F · F· F 10.00% CCGU-3-F 7.00% CBC-33 2.00% CBC-53 2.00%

Example 12

[0137] GGP-3-Cl 12.00% Clearing point [° C.]: +109.0° C. GGP-5-Cl 12.00%Δn [589 nm, 20° C.]: +0.2143 T-3FClF 8.00% V_((10,0,20)) [V]: 1.88PGU-2-F 6.00% PGU-3-F 8.00% FET-2Cl 12 00% FET-3Cl 6.00% CGU-3-F 9.00%BCH-3F · F 6.00% BCH-5F · F 8.00% CCGU-3-F 6.00% CBC-33 3.00% CBC-533.00% CBC-55 1.00%

Example 13

[0138] GGP-5-Cl 14.00% Clearing point [° C.]: +111.0° C. T-3FClF 8.00%Δn [589 nm, 20° C.]: +0.2074 PGU-2-F 6.00% V_((10,0,20)) [V]: 1.86PGU-3-F 10.00% PGU-5-F 13.00% FET-2Cl 4.00% FET-3Cl 8.00% CGU-5-F 5.00%BCH-3F · F 4.00% BCH-5F · F 12.00% CCGU-3-F 7.00% CBC-33 3.00% CBC-533.00% CBC-55 3.00%

Example 14

[0139] GGP-5-Cl 12.00% Clearing point [° C.]: < +112.0° C. T-3FClF10.00% Δn [589 nm, 20° C.]: +0.2118 PGU-2-F 6.00% V_((10,0,20)) [V]:2.06 PGU-3-F 11.00% PGU-5-F 13.00% FET-2Cl 5.00% FET-3Cl 8.00% CCGU-3-F6.00% BCH-3F · F 9.00% BCH-5F · F 11.00% CBC-33 3.00% CBC-53 3.00%CBC-55 3.00%

[0140] The entire disclosure of all applications, patents andpublications, cited above, and of corresponding applications GermanPatent Applications DE 19819392.0 and DE 19843582.7 are herebyincorporated by reference.

[0141] The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

[0142] From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. Liquid-crystalline medium based on a mixture of polar compoundshaving positive dielectric anisotropy, characterized in that itcomprises one or more compounds of the general formula I,

in which R is H, an alkyl or alkenyl radical having 1 to 15 carbon atomswhich is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen, it also being possible for one or more CH₂groups in these radicals to be replaced, in each case independently ofone another, by —O—,

 —CO—, —CO—O—, —O—CO— —S—, or —O—CO—C— in such a way that O atoms arenot linked directly to one another, A¹ (a) is a trans-1,4-cyclohexyleneradical in which, in addition, one or more non-adjacent CH₂ groups mayhave been replaced by —O— and/or —S—, or a 1,4-cyclohexenylene radical,(b) is a 1,4-phenylene radical, in which, in addition, one or two CHgroups may have been replaced by N, (c) is a radical from the groupconsisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl,naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl,  where the radicals (a) and (b)may be monosubstituted or polysubstituted by CN, CH₃ or F, Z¹ is —CO—C—,—O—CO—, —CH₂O—, —OCH₂—, CH₂CH₂—, —CF₂O—, —OCF₂ —CH═CH—, —C≡C—, —(CH₂)₄—,—CH═CH—CH₂CH₂— or a single bond, Y is F, Cl, halogenated alkyl, alkenylor alkoxy having 1 to 6 carbon atoms L¹ is H or F, and m is 0 or
 1. 2.Medium according to claim 1, characterized in that it additionallycomprises one or more compounds selected from the group consisting ofthe general formulae II to IX:

in which the individual radicals have the following meanings: R⁰ isn-alkyl, oxaalkyl, fluoroalkyl or alkenyl, in each case having up to 9carbon atoms, X⁰ is F, Cl, halogenated alkyl, alkenyl or alkoxy having 1to 6 carbon atoms, Y¹ to Y⁴ are in each case, independently of oneanother, H or F, r is 0 or
 1. 3. Medium according to claim 2,characterized in that the proportion of compounds of the formulae I toIX together is at least 50% by weight in the total mixture.
 4. Mediumaccording to claim 2, characterized in that the proportion of compoundsof the formula I is from 10 to 50% by weight in the total mixture. 5.Medium according to at least one of claims 2 and 3, characterized inthat the proportion of compounds of the formulae II to IX is from 20 to80% by weight in the total mixture.
 6. Medium according to claim 1 or 2,characterized in that it additionally comprises a compound of theformula I2

in which R and Y are as defined in claim
 1. 7. Medium according to claim6, characterized in that Y is F, OCHF₂ or OCF₃.
 8. Medium according toone of claims 1 to 7, characterized in that it comprises one or morecompounds of the formula I and one or more compounds of the formula

in which

R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9carbon atoms, and L¹ is H or F.
 9. Medium according to one of claims 1to 8, characterized in that it comprises one or more compounds offormula XI

in which R⁰, X⁰, Y¹ and Y² are as defined in claim
 2. 10. A method ofusing a liquid-crystalline medium according to claim 1 which comprisesemploying a liquid-crystalline medium according to claim 1 forelectro-optical purposes.
 11. Electro-optical liquid-crystal displaycontaining a liquid-crystalline medium according to claim 1.